This invention relates to a communication system for use in carrying out communication between a mobile terminal or station and an IP packet terminal located within a connectionless network. Herein, it is to be noted that the mobile terminal is operable in accordance with the Digital cellular method and the IP (internet protocol) while the IP packet terminal carries out communication by the use of a packet.
With recent world wide spread of an internet and a mobile communication network, attention has been directed to a communication system for interconnection between an IP (internet protocol) network and the mobile communication network. The mobile communication network may include a mobile station (MS) and a base station (BS)/a mobile switching center (MSC)/an IWF (interworking function). The BS, the MSC, and the IWF may be collectively called an interworking facility.
In this event, the mobile station (MS) which is used in such a communication system may be operable in accordance with the Digital cellular method (interim standard) protocol prescribed by TIA (Telecommunication Industry Association)/EIA (Electronic Industry Association). Moreover, the mobile station (MS) is also operable in accordance with the IP (Internet Protocol). In this connection, a protocol of the mobile station is specified by a hiearchical structure which includes a relay layer, a link layer, a network layer, and an application layer. Specifically, the relay layer is formed by a Digital cellular method layer and a radio link protocol (RLP) layer defined by the Digital cellular method while the link layer is formed by a point-to-point protocol (PPP) layer. Moreover, the network layer is formed by a TCP (Transmission Control Protocol)/IP (Internet Protocol) layer.
On the other hand, the interworking facility, such as the base station (BS)/the mobile switching center (MSC)/the interworking function (IWF) is located between the mobile station (MS) and the IP network which is a connectionless network. The interworking facility has a protocol composed of the Digital cellular method layer and the RLP layer for the mobile station and a protocol composed of a physical (PHY) layer, a PPP layer, and an IP layer for the IP network.
At any rate, both the mobile station (MS) and the interworking facility are operable in accordance with the RLP prescribed by the Digital cellular method, as mentioned before.
Herein, it is to be noted that so called a high speed packet is defined as a service option 22, 23, 24, and 25 in the IS-95B and IS-707A among the Digital cellular method, so as to realize a connection between a mobile station and the IP network in accordance with the IP protocol.
In addition, it is to be considered that the transmission rate in the mobile communication system is very slow in comparison with the IP network because complex procedures should be executed so as to establish or release a connection and an overhead indispensably occurs to guarantee a radio quality. Taking this into account, the above-mentioned protocol IS-707A includes a RLP version 2 which is defined in connection with the high speed packet (mentioned above) in order to raise a transmission rate in communication with a mobile station. According to the RLP version 2, a plurality of radio channels are multiplexed between a mobile station and an interworking facility so as to improve transmission efficiency and to expand an available bandwidth. More specifically, the radio channels are simultaneously established in parallel between the mobile station and the interworking facility in the RLP version 2 and include, for example, a fundamental channel and first through eighth supplemental channels. The plurality of the radio channels are bundled to be subjected to multiprocessing and to expand the available bandwidth.
It is noted that the radio protocol, such as the RLP version 2, never recognizes, for example, a PPP frame, an IP protocol packet, and the like that belong to an upper layer and that the PPP frame and IP protocol packet are therefore transparently transmitted in accordance with the radio protocol.
Thus, neither consideration is made at all in the radio protocol about the PPP frame on multiprocessing the links nor definition is included in the upper protocol about multiplexing each radio link. Herein, a PPP link control frame, such as an end request frame, an echo request frame, should be transmitted as the PPP frame. On transmitting such a control frame in accordance with the radio protocol, the control frame is mixed with the other PPP frames for user data and multiplexed into radio channels. Such a mix of the control frame and the data frames makes it difficult to quickly detect the control frame on a reception side.
In other words, no guarantee is given about transmitting the control frame defined by the PPP protocol to a reception side, without any adverse influence to other radio channels. For example, let a sequence of PPP frames which includes a specific PPP frame be received by the interworking facility, such as BS/MSC/IWF, and transmitted through a plurality of radio channels to a mobile station in accordance with the radio protocol. The specific PPP frame may be, for example, a PPPLCP (link control protocol) echo request frame. In this event, each of the PPP frames is divided into the plurality of the radio channels. This means that the specific PPP frame is also dispersed or distributed into the plurality of the radio channels and is transmitted in the form of RLP frames to the mobile station.
In this connection, the mobile station should detect the specific PPP frame by decoding the RLP frames sent through the plurality of the radio channels. Such decoding requires complex control processing and complicated protocol processing over the plurality of the radio channels. In addition, a long time is required to execute such complex processing and transmission efficiency is reduced.